The safe propagation of the human race is fundamental to the well being of our society. One need not be a parent to realize the importance of improved medical devices and methods for safely delivering a fetus.
In vaginal deliveries, the fetus is delivered through the birth canal after the cervix of the mother has fully dilated and effaced. Passing the fetus through the birth canal requires that the vaginal muscles be forced to stretch because the fetal head is much larger than the birth canal under normal circumstances.
Some stretching force is applied to the vaginal tissues by the mother herself. The involuntary contractions of the uterus during labor push the fetus (typically the fetal head) into the birth canal thereby stretching the vaginal tissues of the birth canal wall. The stretching force of these involuntary uterine contractions is combined with the stretching force caused by voluntary contractions of the mother's abdominal muscles as the mother tries to push the fetus out of the uterus.
Often the forces described above are not strong enough or are not medically advisable to use in extracting the fetus. Supplementary force may be applied, for example, in conditions of dystocia (i.e., slow or difficult labor or delivery), uterine inertia, maternal exhaustion, maternal distress, or fetal distress.
Supplementary force may be applied with conventional forceps which grasp the fetal head for traction through the birth canal. However, forceps often cause injuries to the fetal head. Forceps also have an awkward rigid shape which often causes maternal discomfort. Thus, fetal vacuum extractors were developed.
In conventional vacuum-assisted deliveries, a fetal vacuum cup is applied to the fetal head so that the center of the cup corresponds as close as possible to the flexion point of the fetal head. Referring to FIG. 11, the "flexion point" 1101 is medically defined as being approximately three centimeters anterior (i.e., towards the fetal face) from the posterior fontanelle 1102 (i.e., the triangular soft spot on the back of the fetal head 1100) along the sagittal suture 1103 (i.e., mid-line). For clarity, the anterior fontanelle 1104 (i.e., the diamond-shaped soft spot on the top of the fetal head 1100) is also shown in FIG. 11.
The positioning of the center of the cup on the flexion point is important to a safe, relatively easy vacuum-assisted delivery. Traction applied along the pelvic axis from a properly positioned vacuum cup promotes proper fetal presentation as the fetus passes through the birth canal.
Often, the fetus malpresents such that the flexion point is pressed against the birth canal walls. For example, the fetus may be high in the birth canal and presenting in the occipitoposterior or occipitolateral positions (hereinafter "high occipitoposterior" and "high occipitolateral", respectively). Proper positioning of the fetal vacuum cup over the flexion point is difficult if the fetus is malpresenting because the vacuum cup must be inserted between the birth canal wall and the occiput. Thus, the centers of the fetal vacuum cups are often not properly applied over the flexion point of malpresenting fetuses.
The maneuverability of the fetal vacuum cup affects the correct application of the vacuum cup over the flexion point of a malpresenting fetus. Factors that affect maneuverability are 1) the depth and profile of the vacuum cup, 2) the diameter of the vacuum cup, and 3) the design of the vacuum cup with regard to the position and pliability of the suction tube.
Several fetal vacuum extractors might conceivably be applied to a malpresenting fetus such as the device described in U.S. Pat. No. 5,810,840 entitled "Vacuum Extractor". The '840 device includes a cup 1202 (FIG. 12) that has a flexible closed top end 1220. In an insertion position, the stem 1204 is angularly disposed relative to the vertical axis 1288 of the cup 1202 such that a portion of the stem 1204 is recessed into the flexible closed top end 1220 of the cup 1202, thereby facilitating insertion of the cup 1202 into the birth canal in the direction 1286. Although the folding of stem 1204 is useful for insertion into the birth canal, the flexible structure of cup 1202 may not be structurally rigid enough to hold its shape when compressed between the flexion point and the birth canal wall. Also, the profile of the cup 1202 is not small enough to easily insert between the birth canal wall and the flexion point. Even once the cup 1202 is in place with the stem 1204 recessed within the cup 1202, the stem 1204 tends towards its original unrecessed position, often detaching (i.e., prying up and popping off) the cup 1202 from the fetal head. Furthermore, the traction force, when applied at an oblique angle, also contributes to cup 1202 detachment.
Another device is disclosed in U.S. Pat. No. 5,019,086 entitled "Manipulable Vacuum Extractor for Childbirth and Method of Using the Same" and is shown in FIG. 13. The stem 1314 includes a flexible portion 1314c which allows the stem 1314 to bend towards the cup 1330 to facilitate insertion into the birth canal. A significant portion of stem 1314 extends perpendicular from the cup 1330 inhibiting insertion of cup 1330 between the flexion point and the birth canal walls. Cup 1330 also suffers from the same detachment issues discussed above for the '840 device but to a greater extent.
Several devices are lower profile but are quite complicated to use. A device described in U.S. Pat. No. 5,803,926 is shown in FIG. 14. Arms 1414 and 1416 are coupled with the sides of cup 1412 to allow easier insertion into the birth canal. The doctor applies traction and manipulates the fetus with arms 1414 and 1416. This device is complicated to operate since the doctor must manipulate the arms with both hands and must coordinate relative motion between arms 1414 and 1416. The doctor thus has no free hand to perform other tasks. This device also tends to lift up one edge of the cup more than the other, thus prying up and popping off the cup from the fetal head.
Another device commonly used for a malpresenting fetus is the Bird posterior cup device 1500 shown in FIG. 15. This device includes a cup 1501, a handle 1502 and a vacuum hose 1503. Though the profile of the device 1500 is relatively low, the handle 1502 and vacuum hose 1503 must be separately manipulated by the doctor. Furthermore, the insertion of the hose 1503 and parts of the handle 1502 into the birth canal can be intrusive and uncomfortable to the mother. Also, the handle 1502 and hose 1503 may interfere with each other when traction is applied.
Therefore, there is a need for a low-profile, easily operated fetal vacuum cup.